1. Field of the Invention
The present invention relates to processes for the preparation of quick cooking and instant rices, and to quick cooking and instant rice products obtainable thereby.
2. Description of Related Art
The references cited hereinafter, each hereby incorporated by reference, pertain to the field of this invention.
Rice is one of the leading food crops of the world, second only to wheat in terms of annual production for food use. It is the main staple food for about 60% of the world""s population. About 90% of the world""s rice is produced and consumed in Asia. Rice is a semi-aquatic, annual grass which can be grown under a broad range of climatic conditions. Cultivated rice is designated as either Oryza sativa L. or Oryza glaberrima Steud. O. Sativa is the predominant species; O. Glaberrima is grown only in Africa on a limited scale.
The gross structure of the mature rough rice grain is shown in FIG. 1 (From Rice: Chemistry and Technology, Edited by Bienvenido O. Juliano, page 18 (1985)). The principle parts of the grain are the hull, pericarp, seed coat, nucellus, embryo, aleurone layer and endosperm. The hull is the outer covering of the caryopsis (brown rice). The hull comprises 18-20% by weight of the rough rice and serves a protective function against insect infestation and environmental fluctuations. Removal of the hull from rough rice by dehulling exposes the rice caryopsis. The outer four morphologically distinct layers of the caryopsis are the pericarp, seed coat (Tegmen), nucellus and aleurone. Along with much of the embryo (germ), these layers comprise the bran portion of the rice grain. Although the aleurone layer is botanically part of the endosperm, it is removed as part of the bran fraction during milling. The bran portion accounts for 5-8% of the brown rice weight and is the most nutritious part of the caryopsis. The cells of the aleurone layer, in particular, consist of many inclusions called protein bodies and lipid bodies. Accordingly, raw untreated milled rice has a reduced nutritional value since the nutrient bran layer is removed.
Cooking rice typically involves allowing the rice to absorb water and heat. For example, rice may be cooked by placing the rice in boiling water for a period of time. Alternatively, rice may become cooked by steaming. Parboiled rice will typically absorb from 65 to 75 weight percent water during cooking. Water is taken up on cooking linearly with time. Hence reducing cooking time reduces water uptake. This is significant, decreasing from 180 grams for 100 grams of dry rice at 18 minutes to 120 at 10 minutes and 100 at 8 minutes. Low water uptake leaves the rice tasting soft on the outside and firm, chalky and uncooked on the inside (water uptake is the weight increase from long dry rice after cooking in excess water for a given time). Water absorption is defined as the weight of cooked rice yields from 100 g of dry rice after a given time.
Cooked rice typically has different mechanical properties compared to the original rice. The extent of cooking necessary for acceptable mouthfeel and taste varies from region to region. In the United States, for example, a softer rice product is often found desirable, whereas Europeans typically desire a harder or firmer rice. The following is a list of terms often used to characterize the mouthfeel characteristics of cooked rice (see Rice: New Evaluation Methods, by Kohlway, page 120):
Raw white rice is not parboiled, but is milled from brown rice in the dry raw state. It generally cooks faster than parboiled rice. Raw white rice typically requires cooking times of around 12-18 minutes. The resultant cooked rice, however, is extremely starchy tasting. It is believed that water and heat enters the individual starch granules within the rice kernels and causes them to swell and burst releasing free molecular starch. This yields a very starchy, pasty feel in the mouth.
Parboiling is the typical method employed for reducing the starchiness of cooked rice. Parboiled rice is usually defined as rice which has been steeped, heat treated and dried. During the heat treatment step of parboiling, the starch in the endosperm of the rice is substantially gelatinized. The parboiling process and the resulting gelatinization of the starch have several beneficial effects. Parboiling allows the nutrients from the bran layer to migrate to the internal portions of the rice before removal resulting in a rice product having enhanced nutritional values. Moreover, parboiled rice is preferred over white (raw/milled) rice by many consumers for its texture, appearance, flavor, aroma and recipe tolerance.
Conventional parboiling processes generally include the steps of: (1) soaking rough (or paddy) rice in 50-70xc2x0 C. water for 2-4 hours to yield a rough rice having a 30-35 weight percent water content; (2) draining the free water from the soaked rice; (3) applying steam heat under pressure for 8 to 20 minutes to effect gelatinization; and (4) drying the steamed rice with hot air to reduce its water content to about 12-14 weight percent water. The dried, parboiled rough rice is then ready for shelling (to remove the hull) and milling to remove the bran.
Parboiling has been an active topic in the patent literature. There have been numerous efforts to improve upon the basic technology. For example, U.S. Pat. No. 5,017,395 teaches an extra predrying step at an elevated temperature. U.S. Pat. No. 4,810,511 prescribes use of microwave energy for partial gelatinization. According to U.S. Pat. No. 4,361,593, the rice starch is not completely gelatinized during steaming, and a tempering step is performed under non-gelatinizing conditions to reduce subsequent rupturing. In U.S. Pat. No. 4,338,344, there is disclosed an inclined enclosed chamber where rice is cooked in hot water in a first zone at a lower end, and then is steamed in a second zone at an upper end.
Although parboiling provides a rice product having these improved characteristics, the resultant parboiled rice is rendered longer-cooking than milled white rice. Most parboiled rice requires emersion-cooking of at least 20 minutes to prepare the parboiled rice to the desired edibility. It appears that the heat treatment involved in the parboiling processing reduces the product rehydrability which renders it harder and thus longer to cook. Another drawback of conventional rice parboiling processes vis-a-vis white rice milling is that they result in stronger bonding of the bran layer to the rice kernel, with the result that more time and energy must be used in the milling step to remove the bran from the surface of the kernel subsequent to the parboiling.
Accordingly, although parboiled rice shows a great degree of improvement in its freedom from starchiness as well as other advantageous properties, these advantages are partly offset to a degree by the increased cooking time required to fully rehydrate the dry parboiled rice to achieve a cooked product.
Therefore, it would be advantageous to provide a parboiled rice product having reduced cooking times. Rice products having faster cooking times have previously been made primarily by methods that incorporate additional steps following the conventional parboiling operation to alter the original shape and/or by chemically changing the structure of the rice. The former including: (a) size reduction, (b) puffing or, (c) extrusion. Examples of the later chemical processes include: (a) enzymatic treatment or (b) rice protein modification. These prior art methods do not provide a rice product having an original natural appearance in size, texture, shape, color, flavor or mouthfeel.
xe2x80x9cSize reductionxe2x80x9d improves cooking times by reducing the thickness of the individual rice kernels. A reduction in the rice thickness reduces the cooking time since the rice kernel becomes fully hydrated quicker. That is, a reduction in thickness reduces the time it takes for moisture to migrate to the center of the rice kernel. U.S. Pat. No. 2,733,147 to Ozai-Durrani relates to a method of preparing a quick cooking rice product by subjecting whole rice, the external portions of which comprise moist and completely gelatinized starch in a completely soluble condition and the internal portions of which comprise starch ranging from a very slight degree of gelatization and pliability to complete gelatinization and pliability, to mechanical compression so that the structure of the grains is modified without reducing the grains to a flaked condition. The patent discloses that for rice soaked and precooked according to the conditions described above, it has been found that the thickness of the grains should be reduced from about 30% to about 80% of their original (or regular rice) thickness in order to provide a rehydrated product having the texture and other characteristics of regularly cooked rice at a reduced cook time. U.S. Pat. No. 5,045,328 to Lewis et al. relates to the compression of parboiled rice with high moisture content by cold-rolling to effect the cooking properties of the rice.
Although the methods relying on xe2x80x9csize reductionxe2x80x9d result in a rice product having reduced cooking times, the product has an unnatural appearance and modified mouthfeel as a result of the altered shape and size. Moreover, these methods require an addition process steps and pieces of machinery (cold-rolling or compression apparatus) to effect the size reduction.
Methods that utilize a xe2x80x9cpuffingxe2x80x9d step decrease the cooking time by increasing the volume of the rice product, thereby decreasing the density. The result is a porous structure that is easily rehydrated. The puffing processes include: (1) atmospheric pressure procedures, which rely on the sudden application of heat to obtain the necessary rapid vaporization of water, and (2) pressure-drop processes, which involve sudden transferring of superheated moist particles into a space at lower pressure. The puffing phenomenon results from the sudden expansion of water vapor (steam) in the interstices of the granule (See Rice, volume II: Utilization, Second Edition, Edited by Bor S. Luh, page 180).
U.S. Pat. No. 2,438,939 to Ozai-Durrani relates to treating rice with moisture and heat in such a way as to gelatinize the starch and cause the grains to soften and swell substantially beyond their original size and then drying the swollen grains in such a manner as to preserve their enlarged size and produce a porous structure throughout the grains as a result of the shrinkage of the internal starch. The process results in a rice product comprising dried, separate, substantially gelatinized rice grains having of the order of twice their original volume and a porous structure capable of ready hydration to individual grains having the soft, palatable character of ordinary cooked rice. U.S. Pat. No. 4,166,868 to Ando et al. relates to frying compressed rice having a moisture content of 8-25% to form a puffed ready-to-eat rice product. U.S. Pat. No. 4,233,327 to Ando et al. relates to puffing and drying pressed rice having a water content of 8-25% by weight by hot air or high frequency dielectric heating to form an instant-cooking rice product.
Although the xe2x80x9cpuffingxe2x80x9d method results in a rice product having improved cooking times, the product has an unnatural appearance and modified mouthfeel as a result of the altered shape, surface texture and size.
Methods involving xe2x80x9cextrusionxe2x80x9d decrease the cooking time of rice by forming a pasta-like substance by extruding a mass of rice product. The resultant extruded product is similar to pasta and has a significantly different appearance and mouthfeel compared to conventional rice.
The above described methods are also disadvantageous since each requires at least one additional step and/or apparatus for the rice processing. The methods involving the reduction of the kernel thickness, for example, require the separate step of compressing the kernels.
Other methods of reducing the cooking times of rice include those described in the following references.
U.S. Pat. No. 4,810,506 to Lewis et al. relates to a process of producing a grain product which comprises subjecting parboiled grains to treatment with a measured quantity of a solution containing water and an enzyme. Preferably, the parboiled grain is subjected to compression while still hot by passing the grain between rollers prior to treatment with the enzyme containing solution.
U.S. Pat. No. 3,879,566 to Cox et al. relates to a process for preparing a quick cooking rice that modifies the protein component of the rice so that water will be more available to the starch component for imbibition and to modify the starch component of the rice to increase its hydrophilic characteristics.
Here, the rice grains are not subjected to mechanical action to modify their physical structure. Instead, molecular or internal structural modification of the chemical components of the rice grain is accomplished by the use of chemicals and heat treatment to facilitate penetration of water into the rice grains during preparation of the quick cooking rice and also during its final cooking to palatable condition. This chemical alteration of the rice can result in a foreign flavor or color in the cooked rice product.
The above-described methods do not provide a quick cooking parboiled rice product having a natural appearance, flavor and/or mouthfeel. The natural appearance is important because, as widely accepted in culinary arts, the first impression of a food is generally visual. That is, the willingness of a person to eat a particular food depends largely on preconceptions as to appealing color and other visual cues. Appearance is an influential quality attribute pre-supposed by people to be an indicator of deteriorative changes undergone by food. Aroma and flavor can also be influential upon smelling and tasting. Thus, an irregular appearance increases the likelihood that a food will be rejected, and this phenomenon jeopardizes the acceptability of rice amongst the majority of rice eating cultures around the world. This is so to an even greater extent if the rice has a foreign flavor as a result of additives used to modify the cooking characteristics of the rice (i.e., enzymes or chemical reagents). It is desired that rice appearance be uniform and natural and that rice flavor be near bland and subtle.
Accordingly, it would be desirable to produce a quick cooking or instant rice having a natural appearance and flavor and a smooth surface texture without substantially altering the size and/or shape of the individual rice kernels and a method of making the same that does not significantly increase the cost and/or complexity in the manufacturing of fast cooked rice.
It is an object of the invention to provide an improved quick cooking or instant rice product and a method of making the same.
It is a further object of the present invention to provide quick-cooking rice having a natural appearance and flavor and improved mouth feel, improved cooking yield, improved integrity of rice and method of making the same.
It is a still further object of the present invention to provide quick cooking rice having a smooth texture.
It is a still further object of the present invention to provide an improved quick cooking or instant rice without significantly adding to the cost and/or complexity of the rice processing or requiring the use of chemical reagents or enzymes.
The foregoing and other objects and advantages of the invention will be set forth in or apparent from the following description.
The invention relates to quick cooking and instant rice products and to methods of making the same. More specifically, the invention relates to a process including the step of mechanically manipulating rice having a high moisture content to result in a rice product having enhanced cooking characteristics. The resultant products have a natural appearance and flavor and improved mouthfeel characteristics, improved cooking yield and integrity of rice. Preferably, the step of mechanical manipulation is achieved by milling high moisture rice. By milling high moisture rice directly or shortly after parboiling, a quick cooking rice is achieved without adding any additional processing steps or using any chemical reagents or additives. The additional steps of conventional quick cook rice processes such as rehydration, compression and hot air puffing can be eliminated. In fact, the present invention simplifies or reduces the costs associated with preparing quick cook or instant rice since the conventional drying and rehydration steps immediately after the parboiling can either be omitted or greatly reduced since the rice is milled while wet.
It has been found, surprisingly, that the present invention substantially reduces the cooking time required compared to the parboiled, dry milled rice. In particular, this process can be used to produce a quick cooking rice that gives an acceptable texture after boiling in water at about 100xc2x0 C. for only 10-12 minutes or less, e.g., 6-10 minutes, more preferably 5-8 minutes. The precise cooking time of the rice depends on certain parameters including the rice variety and the exact moisture content in the wet manipulation step. However, a significant reduction of cooking times is observed for all rice varieties so far tested, and also for moisture contents in the range from above 19% to 32% by weight. The preferred rice varieties include Panda, Pelde, Thaibonnet, Gulfmont, Katy and Cypress.
Another aspect of the invention relates to the formation of an instant rice product produced by additionally subjecting the wet milled rice to puffing to result in a rice product having further reduced cook times. An instant rice product can be achieved without the step of rehydrating the conventionally, dry milled rice since the wet milled rice already has a high moisture level after milling. The resultant instant rice preferably has a cooking time of less than about 8 minutes, advantageously less than about 7 minutes, even better less than 6 minutes and most preferred less than 5 minutes.